Method of electroplating zinc and electrolyte therefor

ABSTRACT

ATTACHED TO AN NH2-CS-NH2 GROUP, R BEING A CARBONACEOUS RADICAL OF A PHENOL-ALDEHYDE OR OF ITS ETHEROXIDE DERIVATIVES.   NH2-C(=S)-NH-N=CH-R   AN ACIDIC ELECTROLYTIC SOLUTION FOR DEPOSITING ZINC ON VARIOUS PARTS COMPRISING, IN A DEMINERALIZED AQUEOUS SUPPORT, A HYDRATED ZINC SULFATE, AN AMMONIUM SULFATE, A THIO-SEMICARBAZONE COMPOUND ATTACHED TO A THIO-UREA GROUP AS A BRIGHTENING AGENT, AND A NON-IONIC MOISTENING AGENT. TO OBTAIN THE BRIGHTENING AGENT, A PHENOL ALDEHYDE IS MADE TO REACT WITH THIO-UREA IN A HYDROALCOHOLIC MEDIUM, A THIOSEMICARBAZIDE COMPOUND IS PREPARED, WHICH IS DISSOLVED IN A HYDROALCOHOLIC SOLUTION AND WHICH IS ADDED TO THE PRODUCT OF THE PHENOL-ALDEHYDE AND THIO-UREA REACTION SO AS TO OBTAIN A COMPOUND OF THE FORMULA:

UnitedStates Patent 3,558,448 METHOD OF ELECTROPLATING ZINC AND ELECTROLYTE THEREFOR Maurice Roger Accaries, Bourg-la-Reine, and Maurice Emile Girard, Paris, France, assignors to Compagnie des Compteurs, Paris, France, a French company No Drawing. Filed Oct. 1, 1968, Ser. No. 764,337 Claims priority, application France, Oct. 18, 1967, 124,825 Int. Cl. C23b 5/12 US. Cl. 204-55 Claims ABSTRACT OF THE DISCLOSURE NHN=CH-R attached to an NH CSNH group, R being a carbonaceous radical of a phenol-aldehyde or of its etheroxide derivatives.

This invention relates to the zinc plating art, and is concerned with the provision of an improved electrolytic solution for zinc plating.

In numerous industries, for instance, in screw-works, small mechanics, electronics, aircraft industries, etc., electrolytic deposits of zinc are generally made from a cyanided bath, the latter having a good penetrating power,

and the addition of organic compounds enables bright deposits to be obtained. On the other hand, these baths have practically no levelling power and have a moderate output. Furthermore, the utilization of such cyanided baths involves problems of treating residual waters.

In the case where a higher speed of depositing is required, acid baths with a fluoborate or sulphate basis are used, but these baths do not allow bright deposits to be obtained, and have a very slight penetrating power.

Also, zinc baths with a pyrophosphate basis have the disadvantage of being expensive and must be employed at high temperature, and baths with a zincate basis present difiicu-lties due to anodic polarisation and formation of mud on the anodes.

The present invention has the object of remedying the greater part of these various disadvantages.

According to the invention, there is introduced, into acidic aqueous electrolytes containing zinc salts, an organic additive which promotes the production of bright and level zinc coatings. The utilization of these acid baths thus eliminates the special treatment of residual waters and enables treatment at ambient temperature. The invention also has the object of introducing, in conjunction with the brightening agent, agents increasing the levelling power of the baths.

The acid electrolytic solution according to the invention is characterized in that it essentially contains:

A zinc salt, such as zinc sulphate,

An alkali metal or ammonium salt, such as ammonium sulphate,

A thio-semicarbazone compound forming the brightening agent.

The brightening agent according to the invention is characterized in that it comprises a compound of the formula:

in which R is an aryl group containing at least one hydroxy, alkyloxy or alkyleneoxy (--O--CH O) group, x is equal either to 0 or 1, y being 1 or 2 and the total x plus y equal to 2, R is hydrogen or The brightening agent can be prepared by condensing (a) an aldehyde of the RCHO form, in which R is an aryl group containing at least one hydroxy, alkyloxy or alkyleneoxy group, with (b) the thio-semicarbazide followed by a condensation of this product with the thiourea for producing a brightening agent of the formula:

On the other hand, the thiourea can firstly be condensed with aromatic aldehyde followed by a condensation of the reaction product with the thiosemicarbazide to give a compound of the formula:

or else again, the thiosemicarbazide can be replaced by dithiocarbamic acid to give compounds according to the Formulas l or 2 above, according to the order of adding the thiourea and the dithiocarbamic acid.

All these reactions can lead to a subsequent substitution on the terminal aminated group to lead to compounds of the following formula, in the case where the thiosemicarbazide (or dithiocarbamic acid) is reacted with the aromatic aldehyde:

or else the formula according to which in the case where the thiourea is first made to react with the aromatic aldehyde:

The RCHO aromatic aldeyhde can have hydroxy substituents, for instance, mono-hydroxybenzaldehyde or dihydroxybenzaldehyde with the hydroxy group in ortho, meta or para position in relation to the aldehyde group. Again, and preferably, the aromatic ring can have other substituents in the form of alkyloxy groups, such as anisaldehyde or alkylene oxide rings such as piperonal, Alternatively, both hydroxy and alkyloxy groups can be present as in vanillaldehyde.

By way of example, there is made to react, in a hydroalcoholic medium, in 1:1 molecular ratio, phenol aldehyde with thiourea during about 4 hours. The thiosemicarbazide derivative dissolved in a hydroalcoholic solution is prepared also in 1:1 ratio, and is added to the product obtained in the first reaction, the operations being effected at a temperature in the region of 30 C. and during about two hours.

The brightening agent thus obtained can be used directly or after purifying. In the latter case, the final condensation product in hydro-alcoholic solution is precipitated by adding a volume of water five or six times the initial volume. After filtering and washing on a filter with a small quantity of alcohol, the precipitate is re-dissolved in a solvent which can be an acetone alcohol mixture.

The electrolytic solution can also contain additional products enabling the brightness area to be increased, i.e., the possibility of utilizing current densities in a relatively wide scope, for instance, between 0.2 and a./dm. Moreover, these additives also improve the polish effect of the deposit. These additives can be utilized in association with the thiosemicarbazone compound mentioned above. Among these products, we can use alone, or in association with non-ionic tensioactive agents, for example, fatty alcohol derivatives and ethylene oxide or fatty acid and ethylene oxide or phenol alcohol and ethylene oxide derivatives especially nonyl-phenol on which to 13 ethylene oxide molecules are condensed. One can also use aliphatic diamines such as diamino ethylene, diamino propylene, diamino diethylene as Well as hexamethylenetetramine.

It has also been noticed that the introduction into the bath of a di-basic or poly-basic cationic surface active agent obtained by the condensation of a fatty acid with a polyamine, being a diamine or a triamine, would also increase the brightness area.

Anionic surface-active products such, for instance, as sulphated alcohols of C8 to C12 chain length, or their salts, can also be used in the composition of the electrolytic solution in place of the non-ionic surface-active products described above or in association with them.

Another composition also consists of using compounds of the imidazole group, and in particular that obtained by the action of an amine on glyoxal, for example, by action molecule by molecule of CHO--CHO glyoxal on the diethylenetriamine, the reaction taking place at a moderate temperature (40 to 80) in an aqueous medium, the diethylenetriamine being able to be replaced by ethylenediamine or diethylenediamine.

The addition of this compound, while increasing the brightness area reduces the consumption of the primary brightener and has an action such that it can by itself produce a brightness effect in the absence of the primary brightener.

Lastly, it has been noticed that the addition of substances such as ethylenediaminetetracetic acid or its salts, will improve the anodic output and stability of the electrolytic solution.

We give below, by way of non-restictive example, electrolytic solution compositions containing the constituents forming the object of this invention.

The electrolytic solution compositions enumerated in that which follows, apply as well to the electrolysis of parts in bulk in a revolving drum as the electrolysis of parts held fixed in a bath. In the following examples and in the text generally the expression hydrated Zinc sulphate is intended to mean Zn SO -7H O.

EXAMPLE I For depositing zinc on screws in bulk in a drum revolving appreciably at 10 r.p.m., and with a capacity of 50 kg. of parts, 1,000 litres of an aqueous electrolytic solution was used, containing:

150 g./l. of hydrated zinc sulphate 50 g./l. of ammonium sulphate S g./l. of ethylene-diamine 5 g./l. of hexamethylenetetramine 10 g./l. of N-octyl sodium sulphate 0.5 g./l. of the above-mentioned brightening agent 0.3 g./l. of imidazole compound Bath temperature: 22 C.

Current density: 1.5 a./dm.

Anodic surface ratio on cathodic surface l/ 1 Treatment time: 30 minutes Anode soluble in zinc EXAMPLE II For depositing zinc on a television frame, we utilized for preparing the electrolytic solution:

150 g./l. of hydrated zinc sulphate 30 g./l. of ammonium sulphate g./l. de citric acid 10 g./l. of N-octyl sodium sulphate 0.5 g./l. of the above-mentioned brightening agent Bath temperature: 20 C.

Current density: 2 a./dm.

Anodic surface ratio on cathodic surface 1/1 Treatment time: 20 minutes Anode soluble in zinc EXAMPLE III This test was carired out as described in example II, but the anionic moistening agent was replaced by 2 g./l. of nonionic moistening agent obtained by condensing ethylene oxide on a C18 fatty acid with 30 groups of ethylene oxide per molecule.

EXAMPLE IV For a zinc deposit on a television frame, there was utilized:

250 g./l. of hydrated zinc sulphate 50 g./l. of ammonium citrate 10 g./l. of hexamethylenetetramine l g./l. of a di-basic or polybasic cationic surface active agent obtained by reaction of a stearic acid of C18 on a diamine diethylene.

l0 g./l. of N-octyl sodium sulphate 0.5 g./l. of the above-mentioned brightening agent Bath temperature: 22 C.

Current density: 3 a./dm.

Anodic surface ratio on cathodic surface 1/1 Treatment time: 15 minutes Anode soluble in zinc EXAMPLE V We proceeded exactly as in Example IV but the ammonium citrate was replaced by 50 g./l. of ammonium chloride.

EXAMPLE VI For a zinc deposit on screws as in Example I, we utilized:

g./l. of hydrated zinc sulphate 200 g./l. of ammonium sulphate 20 g./l. of hexamethylenetetramine 5 g./l. of the disodium salt of ethylenediaminetetracetic acid 10 g./l. of N-octyl sodium sulphate 0.5 g./l. of the above-mentioned brightening agent Bath temperature: 18 C.

Current density: 1 a./dm.

Anodic surface ratio on cathodic surface 1/ 1 Treatment time: 30 minutes Anode soluble in zinc It was noticed in carrying out the preceding examples that the best results were obtained by baths whose temperature was preferably between 15 and 22 C. without ever exceeding 30 C., the Water used being demineralized and the pH of the electrolytic solutions being in the region of 4 to 4.5.

Various other examples have shown that equally satisfactory results were obtained by modifying, to a somewhat large extent, the quantities of some of the products utilized. For instance, the content of the brightening agent may be from 0.2 to 0.6 grams per liter and the content of the dispersing agent may be from 2 to 6 grams per liter. In particular, the results were not appreciably altered by varying the quantity of zinc sulphate in a bracket of 100 to 250 g./l. and the ammonium sulphate or the ammonium chloride in a bracket of 50 to 200 g./l., taking the quantities into account indicated for the other products.

We claim:

1. An electroplating bath for producing bright deposits of zinc comprising,

in an aqueous acid solution of zinc sulphate and an inorganic salt of an alkali metal selected from the group consisting of ammonium sulphate, ammonium chloride and ammonium citrate,

as a brightening agent a significant amount of an organic compound of the thiosemicarbazone type having the following general structural formula:

in which R is an arylic radical comprising at least one member of the group consisting of OH, O.CH and -OCH O; x is selected from the group consisting of O and 1 and y is selected from the group consisting of 1 and 2, the sum of x+y being 2; R is hydrogen, and

as a complementary additive: a significant amount of surface-active dispersing agent selected from the group consisting of non-ionic and anionic wetting agents.

2. An electroplating bath according to claim 1 in which the surface-active dispersing agent is a non-ionic wetting agent consisting of the condensation product of a fatty acid having 18 carbon atoms per molecule with 30 moles of ethylene oxide.

3. An electroplating bath according to claim 1 in which the surface dispersing active agent is sulphated octyl alcohol used at a concentration of g./l.

4. An electroplating bath according to claim 1 in which R is the radical of aldehyde methylene pyrocatechic (piperonal) 5. An electroplating bath according to claim 1 in Which x=1, y=l, the radical (N-NHCS-NH) resulting from reacting thiosemicarbazide with piperonal.

6. An electroplating bath according to claim 1, wherein the surface active dispersing agent is the condensation product of nonylalcohol with from 10 to 13 moles of ethylene oxide.

7. Method of electroplating a bright deposit of zinc on a metal object, which comprises passing electric current through said object as cathode immersed in a bath, said bath comprising an aqueous acidic solution of a zinc salt, an inorganic salt of an alkali metal of the group consisting of ammonium sulphate, ammonium chloride and ammonium citrate,

as a brightening agent a significant amount of an organic compound of the thiosemicarbazone type having the following general structural formula:

in which R is an arylic radical comprising at least one member selected from the group consisting of OH, O--CH and OCH O; x is 0 or 1 and y is 1 or 2, the sum of x and y being 2; and R is hydrogen, and

as a complementary additive: a significant amount of surface-active dispersing agent selected from the group consisting of non-ionic and anionic wetting agents, said bath being maintained at a temperature of at least 15 C. but not exceeding 30 C., the current density being from about 0.2 to about 5 amperes per square decimeter.

8. Method according to claim 7 in which R is the radical of the aldehyde methylene pyrocatechic (piperonal).

9. Method according to claim 7 in which x=l, 31:1, and the radical (N-NHCSNH) is the product resulting from reacting thiosemicarbazide with piperonal.

10. A method according to claim 7, in which the aqueous bath is maintained at a temperature bteween 15 and 30 C. and contains the zinc salt in a concentration between 100 and 250 grams per liter, the content of alkali metal salt is to 200 grams per liter, the content of brightening agent is 0.2 to 0.6 gram per liter, the dispersing agent content is 2 to 6 grams per liter, a current density of between 0.2 and 5 amperes per square decimeter being utilized.

References Cited UNITED STATES PATENTS 2,384,300 9/1945 Harford 204 2,700,646 1/ 1955 Chester 20444 2,849,352 -8/ 1958 Kirstahler et a1. 20444 2,910,413 10/ 1959 Strauss et al. 204-44 3,005,759 10/ 1961 Safranek et a1. 20455 FOREIGN PATENTS 1,269,855 6/1968 Germany 20455 GERALD L. KAPLAN, Primary Examiner US. Cl. X.R. 

